- Question 4 A Explain The Three Processes Of Fatigue Initiation And Stage I And Ii Crack Growth In A Specimen With An I 1 (369.39 KiB) Viewed 23 times
Question 4. a) Explain the three processes of fatigue initiation and Stage I and II crack growth in a specimen with an ideal surface (i.e no pre-existing cracks). [6 marks] b) Define what is meant by the R-ratio during a fatigue test. Draw a schematic of stress vs time for a loading cycle where R=-0.5. Indicate the stress range, peak stress and mean stress. [5 marks] c) List three methods of improving the fatigue performance of a component and describe the mechanism by which the improvement occurs. [6 marks] d) The following figures show two fracture surfaces (A and B) containing features that are commonly observed during fatigue failure. Name the features observed in both figures, describe their characteristics in relation to fatigue loading and explain in which stage of fatigue do they occur and how. A B [8 marks] 10μm 1mm